The present invention relates to electronic switches, and more particularly to a crosstalk reduction circuit for reducing the coupling of undesired signals to any given output of the switches.
Electronic equipment has been in use for many years to allow the switching of any chosen input signal, either digital or analog, to one or more output ports. A switching array inside the equipment has a variety of hardware devices, called crosspoints, such as relays, field effect transistors (FETs), digital circuits and the like. However the coupling of undesired signals to any given output port, a phenomenon called "crosstalk", is a persistent problem in all such systems.
The unwanted voltage signals couple through a crosspoint matrix to a given output of the matrix through several mechanisms. Any given switch in the matrix has primarily capacitive coupling from input to output through the switch when the switch is "off". Additionally unwanted coupling capacitance exists between inputs and also between outputs. Finally with integrated circuit crosspoints there is a capacitance between each output port and a common voltage level that also produces unwanted crosstalk. Fortunately for most designs the impedance on the input side is so low that this coupling path between inputs can be neglected. Also the capacitive coupling directly between outputs is negligible compared to the coupling from input to output and between output and the common level.
Currently efforts to reduce crosstalk to acceptable levels have relied upon fabricating crosspoints with better "off" isolation characteristics. Also minimizing unwanted electromagnetic coupling inside the equipment through careful circuit layout is necessary in some applications. However none of these efforts really address the major contributors to the crosstalk problem discussed above.
What is desired is a crosstalk reduction circuit for reducing the coupling of undesired signals to any given output port of a switching array.